1. Field of the Invention
The present invention relates to refrigerant handling systems and, in particular, to systems for recovering and recycling refrigerant from a cooling system and recharging recycled refrigerant to the cooling system. The invention has particular application to techniques and apparatus for purging non-condensables from the recovered refrigerant.
As used herein "recover" means to remove used refrigerant from equipment and collect it in an appropriate external container. "Recycle" means to reduce the amount of contaminants in used refrigerant so that it can be reused.
2. Description of the Prior Art
Heretofore, when refrigerant-charged refrigeration systems, such as automotive air conditioning systems, were repaired, the refrigerant charge was simply vented to atmosphere to accomplish the repairs. More recently, it has become increasingly important to capture and reuse the refrigerant charge in such refrigeration systems, both to avoid pollution of the atmosphere and to minimize the increasing costs of disposal and replacement of the refrigerant charge.
Means are available for recycling impure, recovered refrigerant and for recharging the recycled refrigerant into the refrigeration system after service or repairs thereto have been completed. One type of impurity which must be removed from recovered refrigerant is non-condensable material, such as air, which can infiltrate the refrigeration system as a result of leaks or the like. The non-condensables can be vented to atmosphere, but care must be taken that, in the process, minimal refrigerant is vented, in order to assure compliance with governmental pollution control regulations. Prior refrigerant recycling systems have utilized manual vent valves, but manual venting of the non-condensables is time-consuming and inaccurate. Some prior systems have utilized automatic venting mechanisms, wherein diaphragm valves are cyclically opened and closed, but such systems are inaccurate, since the valve operation is not related to the amount of non-condensables in the recovered refrigerant.
It is known that refrigerants have characteristic saturation vapor pressures that vary as associated functions of temperature, as long as refrigerant is present in both liquid and vapor phases, such as in the refillable recycled refrigerant vessel of a refrigerant recycling system. If air or other non-condensables are present in the recycled refrigerant vessel, a differential pressure above the saturation pressure is created, which is proportional to the quantity of non-condensables. Certain prior systems have utilized this relationship for automatically venting the non-condensables. More specifically, the ideal saturated pressure of the refrigerant at a given temperature is determined, and when the actual measured pressure of the refrigerant exceeds that ideal by a predetermined amount, a venting valve is opened. One such arrangement is disclosed in U.S. Pat. No. 5,189,889, in which the vent valve is opened for a predetermined short period of time, typically less than a second, and the process is repeated at varying intervals until the measured pressure drops below the critical level. This purging operation can be relatively time consuming, since the purge valve is open a very small percentage of the time.
Another difficulty with such prior systems is that the pressure sensors required to monitor the actual pressure of the recovered refrigerant are difficult to calibrate. Since calibration requires exposure of the pressure transducer to atmosphere, calibration typically requires disconnection of the pressure transducer from the remainder of the system, which is a time consuming and inconvenient operation.